The invention relates to a laser amplifying system comprising a solid-state member which is of a plate-like design, has flat sides located opposite one another and comprises a laser-active material, a laser radiation field which passes through the solid-state member, a pumping radiation field pumping the laser-active material, a cooling device which absorbs heat from the solid-state member via a first flat side by means of a fluid cooling medium flowing in it and a reflector for the laser radiation field which is arranged on the first flat side.
A laser amplifying system of this type is known from European patent application 0 632 551.
In the case of such a laser amplifying system, the solid-state member is fixed in position via the first flat side bearing the reflector, wherein it is a problem to fix the solid-state member in a defined manner and aligned in such a manner that optical conditions which are as optimum as possible are present for the propagation of the laser radiation field.
The object underlying the invention is therefore to improve a laser amplifying system of the generic type in such a manner that the solid-state member may be arranged and aligned in as optimum a manner as possible.
This object is accomplished in accordance with the invention, in a laser amplifying system of the type described at the outset, in that a support with a stable shape is provided for the solid-state member, this support having the laser radiation field passing through it and being transparent for it, that the solid-state member is supported areally on a support surface of the support with a stable shape with its second flat side and is arranged so as to be defined in its shape and position essentially only via the support surface interacting with the second flat side.
The advantage of the inventive solution is to be seen in the fact that, with this solution, the cooling may be decoupled from the qualitatively high-standard, optical arrangement of the solid-state member relative to the laser radiation field since the cooling takes place via the second flat side, exactly as known from the state of the art, but the qualitatively high-standard, optical arrangement of the solid-state member is brought about via the second flat side which leads to a dimensionally defined arrangement and at the same time to a positionally defined arrangement of the solid-state member due to the areal support without marginal conditions required for the cooling impairing the shape and position of the solid-state member or being able to affect them as a result.
In this respect, a great advantage of the inventive solution is also to be seen in the fact that negative influences on the optical properties of the solid-state member due to unfavorable mechanical conditions can be avoided as a result of the unilateral predetermination of the shape and the position of the solid-state member.
A particularly favorable solution provides for the first flat side, in the area penetrated by the laser radiation field, to be free from constraining forces predetermined by a surface which is, inherently, mechanically rigid. This solution avoids, in particular, in the area of the solid-state member penetrated by the laser radiation field the build up of mechanical tensions which can, again, negatively influence the optical properties of the solid-state member in the area penetrated by the laser radiation field.
This is of significance, in particular, since an expansion of the solid-state member takes place on account of the heating up of the solid-state member by the pumping radiation field and when the solid-state member is subjected on the first flat side to constraining forces predetermined by a mechanically rigid surface this expansion leads to an impairment of the optical properties of the solid-state member in the area penetrated by the laser radiation field.
In the case of the inventive laser amplifying system there are different possibilities for ensuring that shape and position of the second flat side are clearly predetermined by the support surface of the support.
One advantageous embodiment of the inventive solution provides for the solid-state member to be fixed on the support.
With respect to the fixing between solid-state member and support, the most varied of possibilities are conceivable. For example, it is conceivable to fix the solid-state member on the support at the edges.
A particularly favorable solution provides for the solid-state member to be fixed on the support by a connection effective between the support surface and the second flat side.
Such a connection effective between the support surface and the second flat side may be realized in the most varied of ways.
A particularly favorable solution provides for the connection between the support surface and the second flat side to result due to bonding of support and solid-state member, wherein bonding of support and solid-state member is to be understood as the production of a rigid connection between the solid-state member and the support which can be mechanically stressed.
The provision of a connection between solid-state member and support by bonding has the advantage that no additional material is used which could negatively impair the optical properties of the unit consisting of support and solid-state member.
Another solution provides for the connection between the support surface and the second flat side to be brought about by means of a holding layer. Such a holding layer does have the disadvantage that it possibly leads to an impairment of the optical properties of the unit consisting of support and solid-state member but, on the other hand, it has the advantage that the connection between solid-state member and support may be realized in a simple manner.
In order to optimize the optical properties of the unit consisting of support, solid-state member and holding layer connecting them, it is preferably provided for the holding layer to be adapted with respect to its index of refraction to the index of refraction of the solid-state member.
A particularly favorable solution which, in particular, avoids reflections in the area of the holding layer provides for a difference in the respective indexes of refraction of less than 10xe2x88x922 to exist between the holding layer and the support and/or the holding layer and the solid-state member.
Alternatively or in addition to the adjustment of the index of refraction of the holding layer to the support and/or the solid-state member, a further advantageous solution provides for an antireflection layer to be provided between the holding layer and the support.
Furthermore, it is also advantageous when an antireflection layer is provided between the holding layer and the solid-state member.
Alternatively to the provision of a connection effective directly between solid-state member and support, a further, advantageous embodiment provides for the solid-state member and the support to be fixed in a force-locking manner in the area of the support surface and the second flat side as a result of a pressure acting on the solid-state member in the direction of the support. This solution has the advantage that with it the problems which possibly lead to an impairment of the optical properties of the unit consisting of support and solid-state member can be avoided.
A particularly favorable solution provides for the solid-state member to be acted upon with a force in the direction of the support by way of the cooling medium so that the pressure in the cooling medium itself may be used to generate the force, with which a force-locking fixing of the solid-state member on the support is brought about.
Alternatively thereto, another possibility provides for the solid-state member to be acted upon with a force in the direction of the support in sections so that the solid-state member is fixed on the support by way of force locking due to the solid-state member being acted upon partially.
This may be accomplished, for example, in that the solid-state member is acted upon with a force in the direction of the support in an outer area located outside the laser radiation field. In this case, it is possible, for example, to fix the solid-state member on the support by way of mechanical clamping in this outer area, wherein this has the advantage that as a result of the clamping in the outer area of the solid-state member the optical properties thereof in the area penetrated by the laser radiation field are impaired only to a slight degree or insignificantly.
With respect to the optical properties of the solid-state member which can be achieved, it is particularly favorable when the solid-state member acts on the support with essentially the same force at every point with the area of the second flat side bordering on the partial volume penetrated by the laser radiation field so that on account of this essentially homogeneous action of force the forces acting on the solid-state member and thus influencing, where applicable, its optical properties do not cause any inhomogeneities with respect to the optical properties in the partial volume penetrated by the laser radiation field.
Another possibility of abutting the solid-state member on the support surface in a defined manner provides for the solid-state member abutting on the support surface with the second flat side to act on the support, at least with the area of the second support surface bordering on the partial volume penetrated by the laser radiation field, on account of inner tension. This may be realized by means of different solutions.
For example, it would be conceivable to proceed on the basis of a solid-state member with a plane second flat side and to curve the support surface convexly so that the inner tension, with which the solid-state member can be abutted on the support with its area of the support surface bordering on the partial volume penetrated by the laser radiation field on account of the inner tension, results when the plane flat side is placed on the support surface.
Another solution provides for the second flat side to have a convex curvature prior to being abutted on the support surface and an abutment on an essentially plane support surface or one having a smaller convex curvature to be brought about.
With respect to the temperature profile in the solid-state member, no further details have so far been given. One particularly advantageous solution provides for the temperature to be higher at the second flat side than at the first flat side in the areas of the first and second flat sides penetrated by the laser radiation field.
It is particularly favorable when the solid-state member has a temperature gradient extending essentially exclusively transversely to the flat sides in the volume area penetrated by the laser radiation field.
Furthermore, it is also expedient, particularly in order to avoid the formation of any thermal lens, when the solid-state member is essentially free from any temperature gradient in the volume area penetrated by the laser radiation field in the direction of a surface extension in the direction of the flat sides.
Moreover, it is preferably provided for an altogether negative temperature gradient to occur in the solid-state member in a direction extending transversely to the flat sides and extending from the second flat side to the first flat side.
With respect to the discharge of the heat from the solid-state member, no further details have been given in conjunction with the preceding explanations concerning the individual embodiments. It is, for example, preferably provided for the discharge of heat from the solid-state member to take place via a layer system comprising at least one layer applied to the solid-state member.
Such a layer system could, itself, be cooled indirectly. It is particularly favorable when the layer system is acted upon directly by the fluid cooling medium on a side located opposite the flat side.
In order to prevent the layer system, on account of its mechanical properties, from hindering the areal abutment of the second flat side of the solid-state member on the support surface or from thereby leading to mechanical tensions in the solid-state member, it is preferably provided for the discharge of heat from the solid-state member to the fluid cooling medium to take place exclusively via layers consisting of dimensionally flexible materials.
The term dimensionally flexible materials is to be understood such that the rigidity of the layer system is intended to be considerably less than the rigidity of the support and the solid-state member in order not to cause any negative effects.
With respect to the heat conductivity, it is particularly favorable when the layers, via which the discharge of heat from the solid-state member to the fluid cooling medium takes place, to have altogether a heat resistance of at the most 8 Kxc3x97mm2/W.
With respect to the construction of the layer system, the most varied of possibilities are conceivable.
The simplest possibility provides for the layer system to have a single layer which represents a reflector layer which, for its part, is acted upon directly by the cooling medium on its rear side facing away from the first flat side.
It is, however, even more advantageous when the heat discharge is brought about by the cooling device via a cover layer which is borne by a reflector layer and is acted upon by the fluid cooling medium on a side facing away from the solid-state member.
This cover layer is preferably designed as a protective layer for the reflector layer against action of the cooling medium.
In this respect, the cover layer itself can have the most varied of properties. In this respect, it is particularly favorable when no shape-defining action on the solid-state member takes place via the cover layer, i.e. the mechanical properties of the cover layer have no shape-defining effects on the solid-state member at all.
In this respect, the cover layer is preferably designed as a flexible layer.
In order to avoid, as far as possible, the shape-defining action of the cover layer on the solid-state member, it is preferably provided for the cover layer to be designed as a layer adapting in shape to the shape of the solid-state member.
Another preferred solution provides for the layer system to comprise a membrane which is acted upon by the fluid cooling medium on its side facing away from the solid-state member.
A protection of the solid-state member and of the reflector may be achieved in a particularly simple manner with a membrane of this type.
In this respect, the membrane preferably abuts on a side located opposite the solid-state member on the reflector layer or a cover layer applied to the reflector layer.
With respect to as optimum an integration as possible of support, solid-state member and cooling device it is preferably provided for the solid-state member to limit a chamber guiding the cooling medium with the layer system.
In this respect, it is conceivable for this to be brought about solely by way of the solid-state member with the layer system or also by the combination of the solid-state member with the support supporting the solid-state member in a dimensionally defined manner.
A further, advantageous design provides, in particular, for a layer of the layer system to limit the chamber guiding the cooling medium.
This may be, for example, either the cover layer or the membrane.
Furthermore, it is provided for as advantageous an integration as possible of the arrangement of the solid-state member via the support and the cooling device for the cooling chamber for the cooling medium to be provided in a holder housing of a holder for the support so that the holder for the support also acts at the same time as a cooling device.
A particularly favorable solution provides for the support to close an opening in the holder housing with the solid-state member, wherein a recess which forms the cooling chamber extends proceeding from the opening.
With respect to the design of the material for the support, no further details have so far been given. The support does not serve primarily for cooling the solid-state member. Nevertheless, it is preferably provided, in particular, for the good temperature compensation on the part of the support for the support to be formed from a material with a heat conductivity of less than 2 W/mxc3x97K.
A further, advantageous solution provides for the support to be formed from an athermal, optical material, i.e., a material, with which the optical properties are not essentially altered by variations in temperature or temperature gradients since the index of refraction alters with the temperature and the geometry such that the optical properties are essentially not changed.
Since it is not desired within the scope of the inventive solution for the solid-state member to be cooled via the support, it is preferably provided for the support to be essentially thermally insulated in relation to the cooling device.
This may be achieved, for example, by means of insulating spacer members or an insulating layer.
With respect to the structure of support and solid-state member, no further details have so far been given. One advantageous embodiment provides, for example, for the support and the solid-state member to have similar materials forming a crystal grating so that their thermal expansion is as similar as possible and, therefore, no greatly differing heat expansion relative to the support occurs during the heating up of the solid-state member.
With respect to the optical properties of the solid-state member which are as good as possible, it is preferably provided for the flat sides of the solid-state member to be polished so as to be plane-parallel so that, as a result, no negative influence of the laser radiation field during its passage through the flat sides results.
Alternatively thereto, it is preferably provided for the support and the solid-state member to be connected to one another in the area of the second flat side and the support surface and for the first flat side and a front face of the support located opposite the support surface to be polished so as to be plane-parallel in relation to one another so that, in this case, the unit consisting of support and solid-state member has two plane-parallel surfaces which are advantageous for a good beam quality of the laser radiation field.
The support could, in one embodiment, also make contributions to the laser amplifying function, wherein these functional contributions are dominated by those of the laser-active medium.
The material of the support could, for example, have low amplifying properties for the laser radiation field.
In general, the functional contributions of the support are such that the heat input caused by this amounts to less than approximately 10%, even better less than approximately 5%, of the heat input in the laser-active medium.
Further features and advantages of the invention are the subject matter of the following description as well as the drawings illustrating several embodiments. In the drawings:
FIG. 1 shows a longitudinal section through a first embodiment of an inventive laser amplifying system;
FIG. 2 shows an enlarged, sectional illustration of the area A in FIG. 1;
FIG. 3 shows a more enlarged illustration of the section similar to FIG. 2 through a solid-state member of the inventive laser amplifying system with illustration of isotherms;
FIG. 4 shows a section similar to FIG. 2 through a second embodiment;
FIG. 5 shows a section similar to FIG. 2 through a third embodiment;
FIG. 6 shows a section similar to FIG. 1 through a fourth embodiment;
FIG. 7 shows a section similar to FIG. 1 through a fifth embodiment;
FIG. 8 shows a section similar to FIG. 1 through a sixth embodiment;
FIG. 9 shows a section similar to FIG. 1 through a seventh embodiment;
FIG. 10 shows a section similar to FIG. 1 through an eighth embodiment;
FIG. 11 shows a section similar to FIG. 1 through a ninth embodiment.